Method and system for automatic gain control during signal acquisition

ABSTRACT

The disclosure is directed to a mobile communication device that includes automatic gain control (AGC) circuitry and operates in either a tracking mode or an acquisition mode. A received signal is sampled n times to calculate an energy estimate that is used to set the gain control values within the AGC circuitry. The value of n varies depending on whether the handset is operating in the acquisition mode or the tracking mode. Acquisition mode is typically considered to be the mode prior to coarse timing acquisition, also referred to as frame acquisition.

BACKGROUND

1. Field

The present disclosure relates generally to telecommunications, and moreparticularly, to systems and methods to support a mobile communicationsdevice capable of communicating via a wireless broadcast network.

2. Background

Wireless and wireline broadcast networks are widely deployed to providevarious data content to a large group of users. A common wirelinebroadcast network is a cable network that delivers multimedia content toa large number of households. A cable network typically includesheadends and distribution nodes. Each headend receives programs fromvarious sources, generates a separate modulated signal for each program,multiplexes the modulated signals for all of the programs onto an outputsignal, and sends its output signal to the distribution nodes. Eachprogram may be distributed over a wide geographic area (e.g., an entirestate) or a smaller geographic area (e.g., a city). Each distributionnode covers a specific area within the wide geographic area (e.g., acommunity). Each distribution node receives the output signals from theheadends, multiplexes the modulated signals for the programs to bedistributed in its coverage area onto different frequency channels, andsends its output signal to households within its coverage area. Theoutput signal for each distribution node typically carries both nationaland local programs, which are often sent on separate modulated signalsthat are multiplexed onto the output signal.

A wireless broadcast network transmits data over the air to wirelessdevices within the coverage area of the network. However, a wirelessbroadcast network can differ from a wireline broadcast network inseveral key regards. One way in which the two types of networks differis that mobile handsets may encounter service disruptions, or otheractivity, that requires them to acquire, reacquire or resynchronize withthe broadcast signal being transmitted within the wireless broadcastnetwork. In doing so, the receiver of the mobile handset will typicallyemploy automatic gain control (AGC) within its receiver circuits whenacquiring and tracking the broadcast signal. While the concept of AGChas been previously addressed in various wireless networks in differentways, there remains the need for methods and techniques to improve thecost, efficiency, and accuracy of AGC methods and techniques withinwireless broadcast networks.

SUMMARY

One aspect of a mobile communications device relates to a receiverincluding automatic gain control circuitry. The receiver is configuredto receive a broadcast signal from a wireless broadcast network, andoperate in either an acquisition mode or a tracking mode. Furthermore,the automatic gain control circuitry is configured to set a gain controlvalue based on a first number of samples of the received broadcastsignal when the receiver is operating in the acquisition mode and asecond number of samples of the received broadcast signal when thereceiver is operating in the tracking mode.

Another aspect of a mobile communications device relates to a method forautomatic gain control in the mobile communications device. Inaccordance with this method, a broadcast signal is received from awireless broadcast network and the device is operated in either anacquisition mode or a tracking mode. A gain control value is set basedon a first number of samples of the received broadcast signal whenoperating in the acquisition mode and on a second number of samples ofthe received broadcast signal when operating in the tracking mode.

Yet another aspect of a wireless communications device relates to areceiver configured to receive a broadcast signal from a wirelessbroadcast network, and operate in either an acquisition mode or atracking mode. Additionally, included are means for setting a gaincontrol value based on a first number of samples of the receivedbroadcast signal when the receiver is operating in the acquisition modeand on a second number of samples of the received broadcast signal whenthe receiver is operating in the tracking mode.

Still a further aspect of a mobile communications device relates to areceiver having automatic gain control circuitry. The receiver isconfigured to receive a broadcast signal from a wireless broadcastnetwork, and operate in either an acquisition mode or a tracking mode.The automatic gain control circuitry is configured to set a gain controlvalue periodically at a first rate when the receiver is operating in theacquisition mode and periodically at a second rate when the receiver isoperating in the tracking mode.

It is understood that other embodiments of the present invention willbecome readily apparent to those skilled in the art from the followingdetailed description, wherein it is shown and described only variousembodiments of the invention by way of illustration. As will berealized, the invention is capable of other and different embodimentsand its several details are capable of modification in various otherrespects, all without departing from the spirit and scope of the presentinvention. Accordingly, the drawings and detailed description are to beregarded as illustrative in nature and not as restrictive.

BRIEF DESCRIPTION OF THE DRAWINGS

Various aspects of a wireless communications system are illustrated byway of example, and not by way of limitation, in the accompanyingdrawings, wherein:

FIG. 1A illustrates an exemplary wireless broadcast network inaccordance with the principles of the present invention;

FIG. 1B depicts a flowchart of an exemplary method of controlling AGCcircuitry;

FIG. 1C depicts a system in which the exemplary method of FIG. 1B may beimplemented;

FIG. 2 an exemplary superframe that can be used to provide contentwithin a wireless broadcast network such as that of FIG. 1;

FIG. 3 depicts a functional diagram of AGC circuitry within a mobilehandset for use in a wireless broadcast network;

FIG. 4 depicts a conceptual view of different signal levels and gaincontrol settings applied thereto; and

FIG. 5 depicts a block diagram of a wireless broadcast base station andhandset.

DETAILED DESCRIPTION

The detailed description set forth below in connection with the appendeddrawings is intended as a description of various embodiments of theinvention and is not intended to represent the only embodiments in whichthe invention may be practiced. The detailed description includesspecific details for the purpose of providing a thorough understandingof the invention. However, it will be apparent to those skilled in theart that the invention may be practiced without these specific details.In some instances, well known structures and components are shown inblock diagram form in order to avoid obscuring the concepts of theinvention.

Techniques for broadcasting different types of transmissions (e.g.,local and wide-area transmissions) in a wireless broadcast network aredescribed herein. As used herein, “broadcast” and “broadcasting” referto transmission of content/data to a group of users of any size and mayalso be referred to as “multicast” or some other terminology. Awide-area transmission is a transmission that may be broadcast by all ormany transmitters in the network. A local transmission is a transmissionthat may be broadcast by a subset of the transmitters for a givenwide-area transmission. Different local transmissions may be broadcastby different subsets of the transmitters for a given wide-areatransmission. Different wide-area transmissions may also be broadcast bydifferent groups of transmitters in the network. The wide-area and localtransmissions typically carry different contents, but thesetransmissions may also carry the same content.

FIG. 1 shows a wireless broadcast network 100 that can broadcastdifferent types of transmission such as, for example, wide-areatransmissions and local transmissions. Each wide-area transmission isbroadcast by a set of base stations in the network, which may includeall or many base stations in the network. Each wide-area transmission istypically broadcast over a large geographic area. Each localtransmission is broadcast by a subset of the base stations in a givenset for a given wide-area transmission. Each local transmission istypically broadcast over a smaller geographic area. For simplicity, thelarge geographic area for a wide-area transmission is also called a widecoverage area or simply a “wide area”, and the smaller geographic areafor a local transmission is also called a local coverage area or simplya “local area”. Network 100 may have a large coverage area such as theentire United States, a large region of the United States (e.g., thewestern states), an entire state, and so on. For example, a singlewide-area transmission may be broadcast over the entire state ofCalifornia, and different local transmissions may be broadcast overdifferent cities such as Los Angeles and San Diego.

For simplicity, FIG. 1A shows network 100 covering wide areas 110 a and110 b, with wide-area 110 a encompassing three local areas 120 a, 120 b,and 120 c. In general, network 100 may include any number of wide areaswith different wide-area transmissions and any number of local areaswith different local transmissions. Each local area may adjoin anotherlocal area or may be isolated. Network 100 may also broadcast any numberof different types of transmission designated for reception overgeographic areas of any number of different sizes. For example, network100 may also broadcast a venue transmission designated for receptionover a smaller geographic area, which may be portion of a given localarea.

One example of such a broadcast network is the QUALCOMM MediaFLO™network that delivers a programming lineup with a bit rate of about 2bits per second per Hz. The technology used is an orthogonal frequencydivision multiplexing (OFDM)-based air interface designed specificallyfor multicasting a significant volume of rich multimedia content costeffectively to wireless subscribers. It takes advantage of multicastingtechnology in a single-frequency network to significantly reduce thecost of delivering identical content to numerous users simultaneously.Furthermore, the coexistence of local and wide area coverage within asingle RF channel (e.g., 700 MHz) is supported as described above. Thissegmentation between wide area and local area supports more targetedprogramming, local advertising, and the ability to blackout and retuneas required. MediaFLO™ is merely an example of the type of broadcastnetworks described herein and other, functionally equivalent broadcastnetworks are contemplated as well.

Much like cable TV, a subscriber within a wireless broadcast network cansubscribe to different packages and tiers of service (e.g., premiummovies, sports, etc.) that provide them with a set of channels (e.g.,tennis, ESPN, soap operas, BBC, etc.). Different content providersforward the content to the broadcast network which then combines thecontent and broadcast it according to a predetermined schedule. Duringprovisioning of a user's mobile device the capability to receive anddecode the channels to which the user subscribes is programmed into themobile device. The provisioning may be subsequently updated to remove oradd other packages and channels. Thus, there is a broadcast networkoperator that broadcasts a variety of content, but there is also thecarrier (e.g., Verizon, Xingular, etc.), who provisions the handsets,that determine what portions of the content can be subscribed to by auser of the carrier. One of ordinary skill will recognize that thehierarchical arrangement of channels just described is merely oneexample of how to provide multimedia and other content. Otherarrangements and organization of the data and its respective channelsmay be utilized without departing from the scope of the presentinvention.

FIG. 1B depicts a flowchart of exemplary method for controllingautomatic gain circuitry within a mobile handset 190 for use in awireless broadcast network. Details of the high-level flowchart areprovided herein with reference to later figures. In step 148, thereceiving circuitry of the mobile handset 190 receives the broadcastsignal and operates so as to decode and demodulate the received signal.The behavior of the AGC circuitry 198 within the mobile handset 190depends on whether the mobile handset 190 is operating in “tracking”mode or “acquisition” mode. When the mobile handset 190 is powered-up,awakens from an idle mode or sleep, or otherwise must reacquire thebroadcast signal, various parts of the receiver 192 operate inacquisition mode to detect the timing parameters and other informationof the broadcast signal. In general, acquisition mode is the mode inwhich no data packet is being decoded and the system is acquiringfrequency and timing information or, for example, training the AGC.Tracking mode is when data decoding is performed. Thus, the AGCcircuitry 198 can operate in acquisition and tracking mode and thereceiver 192 operates in acquisition mode and data demodulation (ordecode) mode.

Thus, in step 150, a determination is made using a mode determiner 194whether the AGC circuitry of the mobile handset 190 is attempting toacquire the power of the broadcast signal or is merely tracking thepower of an already acquired signal. In step 160, the AGC circuitry 198performs an energy estimate of the AGC output signal. An error signalthat is the ratio of a predetermined energy reference to the energyestimate of the AGC output signal is determined using signal estimator196. The energy estimate is typically performed using n samples of theAGC output signal. If n is large, the energy estimate is performed for arelatively large time period as compared to a smaller value for n. Thus,the behavior of the AGC circuitry 198 of the mobile handset 190 may becontrolled by making n a variable value that is dependent on whether theAGC block is in the acquisition mode or the tracking mode.

Based on the error signal from the reference level, the AGC circuitryupdates its gain and also determines whether or not an analog gain statechange command is required, in step 170. If so, the analog gain state ischanged in step 180 and the digital gain of the AGC is adjustedaccordingly. In particular, when a received signal becomes muchstronger, not as much gain is required and the analog gain setting forthe AGC circuitry may be decreased. Alternatively, the analog gainsetting may be increased when a received signal begins to fade.

The specific way in which the broadcast network signals can be arrangedand broadcast can vary greatly without departing from the spirit andscope of the present invention. Additionally, the particular format andencoding of notification messages and control channel information canvary as well. Described below, however, is one particular implementationof a wireless broadcast network within which the method in flowchart 3may be implemented.

More particularly, the data, pilots, and overhead information for localand wide-area transmissions may be multiplexed in various manners. Forexample, the data symbols for the wide-area transmission may bemultiplexed onto a “transmission span” allocated for the wide-areatransmission, the data symbols for the local transmission may bemultiplexed onto a transmission span allocated for the localtransmission, the TDM (time division multiplexed) and/or FDM (frequencydivision multiplexed) pilots for the wide-area transmission may bemultiplexed onto a transmission span allocated for these pilots, and theTDM and/or FDM pilots for the local transmission may be multiplexed ontoa transmission span allocated for these pilots. The overhead informationfor the local and wide-area transmissions may be multiplexed onto one ormore designated transmission spans. The different transmission spans maycorrespond to (1) different sets of frequency subbands if FDM isutilized by the wireless broadcast network, (2) different time segmentsif TDM is utilized, or (3) different groups of subbands in differenttime segments if both TDM and FDM are utilized. Various multiplexingschemes are described below. More than two different types oftransmission with more than two different tiers of coverage may also beprocessed, multiplexed, and broadcast. A wireless device in the wirelessbroadcast network performs the complementary processing to recover thedata for the local and wide-area transmissions.

FIG. 2 shows an exemplary super-frame structure 200 that may be used tobroadcast local and wide-area transmissions in an OFDM-based wirelessbroadcast network. Data transmission occurs in units of super-frames210. Each super-frame spans a predetermined time duration, which may beselected based on various factors such as, for example, the desiredstatistical multiplexing for data streams being broadcast, the amount oftime diversity desired for the data streams, acquisition time for thedata streams, buffer requirements for the wireless devices, and so on. Asuper-frame size of approximately one second may provide a good tradeoffbetween the various factors noted above. However, other super-framesizes may also be used.

For the embodiment shown in FIG. 2, each super-frame 210 includes aheader segment 220, four equal-size frames 430 a through 430 d, and atrailer segment 240, which are not shown to scale in FIG. 2. Table 1lists the various fields for segments 220 and 240 and for each frame230.

Fields Description TDM Pilot TDM Pilot used for signal detection, framesynchronization, frequency error estimation, and time synchronizationTransition Pilot used for channel estimation and possibly time Pilotsynchronization and sent at the boundary of wide-area and localfields/transmissions WIC Wide-Area identification channel - carries anidentifier assigned to the wide-area being served LIC Localidentification channel - carries an identifier assigned to the localarea being served Wide-Area Wide-Area overhead information symbol -carries OIS overhead information (e.g., frequency/time location andallocation) for each data channel being sent in the wide-area data fieldLocal OIS Local overhead information symbol - carries overheadinformation for each data channel being sent in the local data fieldWide-Area Carries data channels for the wide-area transmission DataLocal Data Carries data channels for local transmission

For the embodiment shown in FIG. 2, different pilots are used fordifferent purposes. A pair of TDM pilots 201 are transmitted at or nearthe start of each super-frame and may be used for the purposes noted inTable 1. For example, one of the pilots TDM1 may be used for coarsetiming to detect the beginning of the frame 400, while the other pilotTDM2 may be used to provide a long channel estimate. A transition pilotis sent at the boundary between local and wide-areafields/transmissions, and allows for seamless transition between thelocal and wide-area fields/transmissions.

The local and wide-area transmissions may be for multimedia content suchas video, audio, teletext, data, video/audio clips, and so on, and maybe sent in separate data streams. For example, a single multimedia(e.g., television) program may be sent in three separate data streamsfor video, audio, and data. The data streams are sent on data channels.Each data channel may carry one or multiple data streams. A data channelcarrying data streams for a local transmission is also called a “localchannel”, and a data channel carrying data streams for a wide-areatransmission is also called a “wide-area channel”. The local channelsare sent in the Local Data fields and the wide-area channels are sent inthe Wide-Area Data fields of the super-frame. Thus, within the wide-areadata 241 of a frame 230 b, there are a number of MediaFLO logicalchannels (MLCs) 240 (although only one is depicted in FIG. 2. Each MLCis a logical channel that represents a separate video, audio, or datastream. The local data 243 is also separated into many different logicalchannels 242. When decoding portions of a frame, the mobile device mayreceive and decode only the MLC 240, 242 for which an application isrequesting data. As explained in more detail herein, the timinginformation, or “location” of the MLC 240, 242, is included in theoverhead information (i.e., Wide-Area OIS and Local OIS) of the header220.

Each data channel may be “allocated” a fixed or variable number ofinterlaces in each super-frame depending on the payload for the datachannel, the availability of interlaces in the super-frame, and possiblyother factors. Each data channel may be active or inactive in any givensuper-frame. Each active data channel is allocated at least oneinterlace. Each active data channel is also “assigned” specificinterlaces within the super-frame based on an assignment scheme thatattempts to (1) pack all of the active data channels as efficiently aspossible, (2) reduce the transmission time for each data channel, (3)provide adequate time-diversity for each data channel, and (4) minimizethe amount of signaling needed to indicate the interlaces assigned toeach data channel. For each active data channel, the same interlaceassignment may be used for the four frames of the super-frame.

The Local OIS field indicates the time-frequency assignment for eachactive local channel for the current super-frame. The Wide-Area OISfield indicates the time-frequency assignment for each active wide-areachannel for the current super-frame. The Local OIS and Wide-Area OIS aresent at the start of each super-frame to allow the wireless devices todetermine the time-frequency location of each data channel of interestin the super-frame.

The various fields of the super-frame may be sent in the order shown inFIG. 2 or in some other order. In general, it is desirable to send theTDM pilot and overhead information early in the super-frame so that theTDM pilot and overhead information can be used to receive the data beingsent later in the super-frame. The wide-area transmission may be sentprior to the local transmission, as shown in FIG. 2, or after the localtransmission.

FIG. 2 shows a specific super-frame structure. In general, a super-framemay span any time duration and may include any number and any type ofsegments, frames, and fields. However, there is normally a useful rangeof super-frame durations related to acquisition time and cycling timefor the receiver electronics. Other super-frame and frame structures mayalso be used for broadcasting different types of transmission, and thisis within the scope of the invention.

The pilot signals of FIG. 2 that are transmitted during the broadcasttransmission may be used to derive (1) a channel estimate for thewide-area transmission, which is also called a wide-area channelestimate, and (2) a channel estimate for the local transmission, whichis also called a local channel estimate. The local and wide-area channelestimates may be used for data detection and decoding for the local andwide-area transmissions, respectively. These pilots may also be used forchannel estimation, time synchronization, acquisition (e.g., automaticgain control (AGC)), and so on. The transition pilot may also be used toobtain improved timing for the local transmission as well as thewide-area transmission.

In one particular example, the basic signal unit for the wirelessbroadcast network is an OFDM symbol that consists of 4642 time-domainbaseband samples called OFDM chips. Among these OFDM chips are 4096 datachips. The data chips are cyclically extended with 529 chips precedingthe data portion and 17 chips following the data portion. The first 17chips of an OFDM symbol may overlap the last 17 chips of the OFDM symbolthat precede them. As a result, the time duration of each OFDM symbol is4625 chips long. And may be transmitted for example, at 5.55×10⁶chips/second. Although some of the AGC circuitry described herein isdiscussed with reference to this specific OFDM arrangement, one ofordinary skill will recognize that other values for various OFDM symbolsmay also be used without departing from the scope of the presentinvention.

FIG. 3 depicts a functional-level diagram of exemplary AGC circuitrywithin a receiving portion of a mobile handset. The broadcast signal isreceived by the antenna 302, and may be filtered by a surface acousticwave (SAW) filter 301, amplified by the low noise amplifier (LNA) 301,and passed to down conversion circuitry 304 and optional filteringcomponents 306. At this stage, the signal remains an analog signal butis now a baseband signal. For example, the broadcast signal centered at700 MHz in a MediFLO® network would be converted to a signal between−3−+3 MHz. This signal is then passed to the A/D converter 310 forconversion into digital samples. AGC circuitry 308 provides a feedbackcontrol loop to set a gain level within the down converter 304 and theLNA block. Within the AGC circuitry 308, a digital gain value is appliedby the digital gain application circuitry 312. The resulting signal isthen fed to the other components of the demodulator 316 for furtherprocessing of the signal.

In addition, the resulting signal is provided to an energy estimator anderror signal detector 314 that determines the energy within n chips, orsamples, of the resulting signal and an error signal that is the ratioof a predetermined energy reference to the energy estimate. This errorsignal is passed to an analog and digital gain adjustment block 309 andthen used to adjust both the analog gain value at the downconverter 304as well as the digital gain application 312. One of ordinary skill willrecognize that there are a variety of functionally equivalent methodsand techniques to estimate the energy of a signal and then set a gainvalue accordingly contemplated within the scope of the presentinvention.

As a result of the circuitry of FIG. 3, the gain control values areadjusted every n samples. The specific value of n is determined by theoperating mode of the mobile handset. Thus, TDM pilot processingcircuitry 318 is provided to supply a signal to the AGC circuitry 308indicating whether the broadcast signal has yet to be acquired in termsof coarse timing acquisition and frequency acquisition. During theacquisition phase in which the receiver tries to detect TDM pilot 1 andperform the coarse frequency and timing estimation, it is desirable thatthe signal output of the block 312 be substantially a constant levelbelow the full scale of AGC output. One advantageous level is, forexample, 11 dB below AGC output full scale. If the signal amplitude isvarying a lot and the AGC block 308 does not react fast enough, in someinstances cause a mobile handset to mistakenly declare coarse timingacquisition when none is actually present or fail to properly acquire anexisting signal. By setting the value for n samples to be less duringacquisition mode, the gain of the receiver is potentially updated moreoften because the gain values are updated after every n samples. Thus,having a value of n during acquisition mode that is less than the valueof n used during tracking mode, the AGC circuitry 308 is more responsiveto changes in a signal that has yet to be acquired. Upon receiving theTDM1 detection signal from the TDM pilot processing circuitry 318, theAGC may switch to operate in the tracking mode.

In the exemplary OFDM symbol described above having 4096 data chips, avalue of 256 chips for n provides advantageous results over manydifferent operating conditions of a mobile handset within a wirelessbroadcast network. Thus, during a single OFDM symbol, the AGC gaincontrol values are updated approximately 16 times. In contrast, duringtracking mode, adjustments occurring once every OFDM symbol (i.e., every4625 samples) provide advantageous results. Thus, during acquisitionmode, the feedback loop of the AGC circuitry 308 updates the analog anddigital gain values about 16 times as frequently as when operating inthe tracking mode. As mentioned, this particular relationship (e.g., 16times), provides advantageous improvements in accuracy while acquiringthe TDM pilot signal. However, if for example, more false positives canbe tolerated (which increases power consumption), this relationship maybe lowered to around 8 times as frequent. Furthermore, the number of nsamples selected during acquisition mode may be a function of the totalnumber of samples within an OFDM symbol. Accordingly, if there were 8192data chips in an OFDM symbol, then the AGC gain value updates may be setto occur every 512 samples.

FIG. 4 provides a conceptual diagram of different discrete analog gainvalues within the received signal. In this example, the received signalsare logically separated into four different levels, each levelcorresponding to a different gain value to be applied within the analogcircuitry of AGC. In operation, the AGC circuitry 308 attempts toprovide a signal to the demodulator 316 having a constant power level.For example, the desired, constant power level may be −11 dB from theAGC output full scale. First, the AGC circuitry sets the analog gainvalue to one of four values 402, 403, 404, 405, depending on the currentenergy estimate of the AGC output signal. A received signal in the Level1 402 would require greater amplification than one in the Level 3 rangeand the AGC sets the gain control value accordingly. For example, gainvalues 402-405 may be 53 dB, 37 dB, 22 dB, and 6 dB respectively. Thiscan be thought of as a course gain adjustment of the analog signal thatis applied at the downconverter 304 and the LNA block. However, evenwithin a particular level, the energy estimate may vary in range. Thisvariation is handled by the digital gain adjustment 312 so that itapplies a continuous digital gain based on the current energy estimateto bring the signal to the desired level. This can be thought of as afine gain adjustment. Depending on the value of n samples used tocalculate the energy estimate, the current gain value settings areupdated by the error signal which is the ratio of the most recent energyestimate and the desired reference level, and any changes to thesettings are implemented as needed. The new gain value settings are thenused until the next energy estimate is completed.

FIG. 5 shows a block diagram of a base station 1010 and a wirelessdevice 1050 that may be used to implement the wireless broadcast network100 in FIG. 1. Base station 1010 is generally a fixed station and mayalso be called an access point, a transmitter, or some otherterminology. Wireless device 1050 may be fixed or mobile and may also becalled a user terminal, a mobile station, a receiver, or some otherterminology. Wireless device 1050 may also be a portable unit such as acellular phone, a handheld device, a wireless module, a personal digitalassistant (PDA), and so on.

At base station 1010, a transmit (TX) data processor 1022 receives datafor a wide-area transmission from sources 1012, processes (e.g.,encodes, interleaves, and symbol maps) the wide-area data, and generatesdata symbols for the wide-area transmission. A data symbol is amodulation symbol for data, and a modulation symbol is a complex valuefor a point in a signal constellation for a modulation scheme (e.g.,M-PSK, M-QAM, and so on). TX data processor 1022 also generates the FDMand transition pilots for the wide area in which base station 1010belongs and provides the data and pilot symbols for the wide area to amultiplexer (Mux) 1026. A TX data processor 1024 receives data for alocal transmission from sources 1014, processes the local data, andgenerates data symbols for the local transmission. TX data processor1024 also generates the pilots for the local area in which base station1010 belongs and provides the data and pilot symbols for the local areato multiplexer 1026. The coding and modulation for data may be selectedbased on various factors such as, for example, whether the data is forwide-area or local transmission, the data type, the desired coverage forthe data, and so on.

Multiplexer 1026 multiplexes the data and pilot symbols for the localand wide areas as well as symbols for overhead information and the TDMpilot onto the subbands and symbol periods allocated for these symbols.A modulator (Mod) 1028 performs modulation in accordance with themodulation technique used by network 100. For example, modulator 1028may perform OFDM modulation on the multiplexed symbols to generate OFDMsymbols. A transmitter unit (TMTR) 1032 converts the symbols frommodulator 1028 into one or more analog signals and further conditions(e.g., amplifies, filters, and frequency upconverts) the analogsignal(s) to generate a modulated signal. Base station 1010 thentransmits the modulated signal via an antenna 1034 to wireless devicesin the network.

At wireless device 1050, the transmitted signal from base station 1010is received by an antenna 1052 and provided to a receiver unit (RCVR)1054. Receiver unit 1054 conditions (e.g., filters, amplifies, andfrequency downconverts) the received signal and digitizes theconditioned signal to generate a stream of data samples. A demodulator(Demod) 1060 performs (e.g., OFDM) demodulation on the data samples andprovides received pilot symbols to a synchronization (Sync)/channelestimation unit 1080. Unit 1080 also receives the data samples fromreceiver unit 1054, determines frame and symbol timing based on the datasamples, and derives channel estimates for the local and wide areasbased on the received pilot symbols for these areas. Unit 1080 providesthe symbol timing and channel estimates to demodulator 1060 and providesthe frame timing to demodulator 1060 and/or a controller 1090.Demodulator 1060 performs data detection on the received data symbolsfor the local transmission with the local channel estimate, performsdata detection on the received data symbols for the wide-areatransmission with the wide-area channel estimate, and provides detecteddata symbols for the local and wide-area transmissions to ademultiplexer (Demux) 1062. The detected data symbols are estimates ofthe data symbols sent by base station 1010 and may be provided inlog-likelihood ratios (LLRs) or some other form.

Demultiplexer 1062 provides detected data symbols for all wide-areachannels of interest to a receive (RX) data processor 1072 and providesdetected data symbols for all local channels of interest to an RX dataprocessor 1074. RX data processor 1072 processes (e.g., deinterleavesand decodes) the detected data symbols for the wide-area transmission inaccordance with an applicable demodulation and decoding scheme andprovides decoded data for the wide-area transmission. RX data processor1074 processes the detected data symbols for the local transmission inaccordance with an applicable demodulation and decoding scheme andprovides decoded data for the local transmission. In general, theprocessing by demodulator 1060, demultiplexer 1062, and RX dataprocessors 1072 and 1074 at wireless device 1050 is complementary to theprocessing by modulator 1028, multiplexer 1026, and TX data processors1022 and 1024, respectively, at base station 1010.

Controllers 1040 and 1090 direct operation at base station 1010 andwireless device 1050, respectively. These controllers may behardware-based, software-based or a combination of both. Memory units1042 and 1092 store program codes and data used by controllers 1040 and1090, respectively. A scheduler 1044 schedules the broadcast of localand wide-area transmissions and allocates and assigns resources for thedifferent transmission types.

For clarity, FIG. 5 shows the data processing for the local andwide-area transmissions being performed by two different data processorsat both base station 1010 and wireless device 1050. The data processingfor all types of transmission may be performed by a single dataprocessor at each of base station 1010 and wireless device 1050. FIG. 3also shows the processing for two different types of transmission. Ingeneral, any number of types of transmission with different coverageareas may be transmitted by base station 1010 and received by wirelessdevice 1050. For clarity, FIG. 3 also shows all of the units for basestation 1010 being located at the same site. In general, these units maybe located at the same or different sites and may communicate viavarious communication links. For example, data sources 1012 and 1014 maybe located off site, transmitter unit 1032 and/or antenna 1034 may belocated at a transmit site, and so on. A user interface 1094 is also incommunication with the controller 1090 that allows the user of thedevice 1050 to control aspects of its operation. For example, theinterface 1094 can include a keypad and display along with theunderlying hardware and software needed to prompt a user for commandsand instructions and then to process them once they are received.

The techniques described herein for broadcasting different types oftransmission over the air may be implemented by various means. Forexample, these techniques may be implemented in hardware, software, or acombination thereof. For a hardware implementation, the processing unitsat a base station used to broadcast different types of transmission maybe implemented within one or more application specific integratedcircuits (ASICs), digital signal processors (DSPs), digital signalprocessing devices (DSPDs), programmable logic devices (PLDs), fieldprogrammable gate arrays (FPGAs), processors, controllers,micro-controllers, microprocessors, other electronic units designed toperform the functions described herein, or a combination thereof. Theprocessing units at a wireless device used to receive different types oftransmission may also be implemented within one or more ASICs, DSPs, andso on.

For a software implementation, the techniques described herein may beimplemented with modules (e.g., procedures, functions, and so on) thatperform the functions described herein. The software codes may be storedin a memory unit (e.g., memory unit 1042 or 1092 in FIG. 5) and executedby a processor (e.g., controller 1040 or 1090). The memory unit may beimplemented within the processor or external to the processor, in whichcase it can be communicatively coupled to the processor via variousmeans as is known in the art.

The previous description is provided to enable any person skilled in theart to practice the various embodiments described herein. Variousmodifications to these embodiments will be readily apparent to thoseskilled in the art, and the generic principles defined herein may beapplied to other embodiments. Thus, the claims are not intended to belimited to the embodiments shown herein, but is to be accorded the fullscope consistent with the language claims, wherein reference to anelement in the singular is not intended to mean “one and only one”unless specifically so stated, but rather “one or more.” All structuraland functional equivalents to the elements of the various embodimentsdescribed throughout this disclosure that are known or later come to beknown to those of ordinary skill in the art are expressly incorporatedherein by reference and are intended to be encompassed by the claims.Moreover, nothing disclosed herein is intended to be dedicated to thepublic regardless of whether such disclosure is explicitly recited inthe claims. No claim element is to be construed under the provisions of35 U.S.C. §112, sixth paragraph, unless the element is expressly recitedusing the phrase “means for” or, in the case of a method claim, theelement is recited using the phrase “step for.”

1. A mobile communications device comprising: a receiver configured toreceive a broadcast signal comprising a plurality of OrthogonalFrequency Division Multiplex (OFDM) symbols from a wireless broadcastnetwork, and operate in either an acquisition mode or a tracking mode;and automatic gain control circuitry configured to set a gain controlvalue based on a first number of samples of the received broadcastsignal when the receiver is operating in the acquisition mode, where thefirst number of samples is less than a number of samples for a one ofthe plurality of OFDM symbols, and on a second number of samples of thereceived broadcast signal when the receiver is operating in the trackingmode.
 2. The mobile communications device of claim 1, wherein the firstnumber of samples is less than the second number of samples.
 3. Themobile communications device of claim 1, wherein the second number ofsamples comprises the number of samples for the one of the plurality ofOFDM symbols.
 4. The mobile communications device of claim 1, whereinthe first number of samples comprises a fraction of approximately oneeighth or less of the number of samples of one of the plurality of OFDMsymbols.
 5. The mobile communications device of claim 4, wherein thefirst number of samples comprises one sixteenth or less of one of theplurality of OFDM symbols.
 6. The mobile communications device of claim1, wherein the received broadcast signal includes a TDM pilot signal. 7.The mobile communications device of claim 6, further comprising: aprocessor configured to operate the receiver in the acquisition mode ifthe TDM pilot signal has not been acquired and operate the receiver inthe tracking mode once the TDM pilot signal has been acquired.
 8. Themobile communications device of claim 1, wherein the automatic gaincontrol circuitry is further configured to determine an energy estimateof the received broadcast signal.
 9. The mobile communications device ofclaim 1, wherein the automatic gain control circuitry is furtherconfigured to set the gain control value based on an energy estimate ofthe first number of samples when the receiver is operated in theacquisition mode.
 10. The mobile communications device of claim 1,wherein the automatic gain control circuitry is further configured toset the gain control value based on an energy estimate of the secondnumber of samples when the receiver is operated in the tracking mode.11. The mobile communications device of claim 1, wherein the gaincontrol value comprises a plurality of values.
 12. The mobilecommunications device of claim 1, wherein the gain control valueincludes an analog control value and a digital control value.
 13. Amethod for automatic gain control in a mobile communications device,comprising: receiving a broadcast signal comprising a plurality ofOrthogonal Frequency Division Multiplex (OFDM) symbols from a wirelessbroadcast network; operating in either an acquisition mode or a trackingmode; and setting a gain control value based on a first number ofsamples of the received broadcast signal when operating in theacquisition mode, where the first number of samples is less than anumber of samples for a one of the plurality of OFDM symbols, and on asecond number of samples of the received broadcast signal when operatingin the tracking mode.
 14. The method of claim 13, wherein the firstnumber of samples is less than the second number of samples.
 15. Themethod of claim 13, wherein the second number of samples comprises thenumber of samples for the one of the plurality of OFDM symbols.
 16. Themethod of claim 13, wherein the received broadcast signal includes a TDMpilot signal.
 17. The method of claim 16, further comprising: operatingthe receiver in the acquisition mode if the TDM pilot signal has notbeen acquired; and operating the receiver in the tracking mode once theTDM pilot signal has been acquired.
 18. The method of claim 13, furthercomprising: determining an energy estimate of the received broadcastsignal.
 19. The method of claim 18 further comprising: determining anerror signal which represents a power difference between the energyestimate and a desired reference level.
 20. The method of claim 13,wherein the gain control value comprises a plurality of values.
 21. Awireless communications device having a receiver configured to receive abroadcast signal from a wireless broadcast network, and operate ineither an acquisition mode or a tracking mode, the device comprising:means for estimating a received signal energy of the broadcast signalcomprising a plurality of Orthogonal Frequency Division Multiplex (OFDM)symbols based on a first number of samples of the received broadcastsignal when the receiver is operating in the acquisition mode and on asecond number of samples of the received signal when the receiver isoperating in the tracking mode, wherein the first number of samples isless than a number of samples for a one of the plurality of OFDMsymbols; and means for setting a gain control value based on theestimate of the received signal energy.
 22. A mobile communicationsdevice comprising: a receiver configured to receive a broadcast signalfrom a wireless broadcast network, the broadcast signal comprising aplurality of Orthogonal Frequency Division Multiplex (OFDM) symbols, andoperate in either an acquisition mode or a tracking mode; and automaticgain control circuitry configured to set a gain control valueperiodically at a first rate that is higher than an OFDM symbol ratewhen the receiver is operating in the acquisition mode and periodicallyat a second rate when the receiver is operating in the tracking mode.23. The mobile communications device of claim 22, wherein the first rateis more frequent than the second rate.
 24. A computer-readable memoryunit encoded with a computer program for automatic gain control in amobile communications device, which upon execution cause one or moreprocessors to: receive a broadcast signal comprising a plurality ofOrthogonal Frequency Division Multiplex (OFDM) symbols from a wirelessbroadcast network; operate in either an acquisition mode or a trackingmode; and set a gain control value based on a first number of samples ofthe received broadcast signal when operating in the acquisition mode,where the first number of samples is less than a number of samples for aone of the plurality of OFDM symbols, and on a second number of samplesof the received broadcast signal when operating in the tracking mode.25. The computer-readable memory unit of claim 24, wherein the firstnumber of samples is less than the second number of samples.
 26. Thecomputer-readable memory unit of claim 24, wherein the second number ofsamples comprises the number of samples for the one of the plurality ofOFDM symbols.
 27. The computer-readable memory unit of claim 24, whereinthe received broadcast signal includes a TDM pilot signal.